Fabric moisture detector

ABSTRACT

A fabric moisture detector and method is provided. The detector has a  supt insulating structure, and a pair of electrodes, which have a pair of opposite faces separated by a gap of selective thickness, such as four inches or ten centimeters. The detector also has a current sensor, for measuring the current through the gap during the application of a relatively high voltage, such as about 10,000 volts to 60,000 volts for a ten centimeter gap. The voltage applied using a ten centimeter gap can be between about 1,000 volts per gap centimeter to 6,000 volts per gap centimeter. The process includes the steps of measuring the gap current during the application of the specified voltage, whereby a dry fabric or bare electrodes yields substantially no current and a wet fabric yields a peak current.

GOVERNMENTAL INTEREST

The invention described herein may be made, used or licensed by theGovernment for governmental purposes without the payment of anyroyalties thereon or therefor.

The invention relates to a fabric moisture detector, and in particularthe invention relates to a fabric moisture detector having a pair ofhigh voltage electrodes.

BACKGROUND OF THE INVENTION

The prior art fabric moisture detector included an evaporator and acondenser.

One problem with the prior art fabric moisture detector is therelatively slow operation of the detector.

It is believed that there ia unpublished test data which showsaccelerated drying of fabric wetted with water, when subject to anelectric potential of about 10,000 volts.

SUMMARY OF THE INVENTION

According to the present invention, a fabric moisture detector isprovided. This detector comprises a support structure; a pair ofelectrodes having a space therebetween and having respective conductors;and a heating coil subassembly having a pair of connecting wires:whereby a fabric specimen which is disposed in the space between thepair of spared electrodes is tested for moisture.

By using the pair of spaced electrodes for testing a fabric specimendisposed therebetween, current, which indicates the moisture, ismeasured by a current meter during the application of a high voltagethrough the electrodes.

The foregoing and other objects, features and advantages will beapparent from the following description of the preferred embodiment ofthe invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fabric moisture detector according tothe invention; and

FIG. 2 is a graph for linen wet with water showing electric field alongthe x-axis (v/cm.) versus current (amperes) and E_(V) along the y-axis.

FIG. 3 is a graph for linen wet with liquid showing electric field alongthe x-axis (v/cm. versus current (amperes) and E_(V) along the y-axis.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a moisture or vapor detector or assembly 10 isprovided. Assembly 10 has a support insulating structure 12, and a pairof spaced lower and upper electrodes 14, 16, which have respective lowerand upper conductors 18, 20. Assembly 10 also has a pair of left andright heater coils 22, 24, which have respective wires 26, 28. Coils 22,24 heat the parts of the support structure 12 on which they are wrappedfor preventing condensation and a short circuit around electrodes 14,16.

Support 12 has a vertical wall 30, and a lower horizontal wall 32, whichia fixedly connected to vertical wall 30, and an upper horizontal wall34, which is fixedly connected to vertical wall 30.

vertical wall 30, has three cutouts 36, 38, 40, which form two verticalcoil posts 42, 44, on which respective heater coils 22, 24 are wound.

Lower and upper electrodes 14, 16 have respective lower and upper solidrods 46, 48, and respective lower and upper disks 50, 52, which arefixedly connected to respective rods 46, 48. Rods 46, 48 and disks 50,52 have a common centerline 54.

Lower rod 46 is fixedly connected at its lower end 55 to lowerhorizontal wall. Upper rod 48 extends through a hole 56 in upperhorizontal wall 34. Upper rod 48 is press fit into hole 56, to providevertical movement, when an axial force is applied to rod 48, of rod 48relative to wall 34. Disks 50, 52 have respective faces 58, 60, whichare separated by a gap 62. The size of gap 62 is set by moving upperdisk 52 relative to lower disk 50.

Heater coils 22, 24 are arranged symmetrically about a horizontal axis64. Disk face 58 supports a substrate or sample or specimen 66, which isshown in FIG. 1 in position for a test.

Electrode conductors 18, 20 are connected in series to a voltage sourceor supply 68, and through a current meter 70 for sensing current. Source68 and assembly 10 rest on a table top 72.

Materials and sizes of parts of assembly 10 are indicated hereafter.Rods 46, 48 are composed of stainless steel. Disks 50, 52 are composedof stainless steel. Support 12 is composed of a polystyrene material,which is an electrical insulation material. Gap 62, which is adjustable,has a range of about up to 10 centimeters.

As shown in FIGS. 2 and 3, a number of test curves of water and otherliquids are shown. The curves include:

a dry electrode (B) curve 76 in FIGS. 2 and 3; and

a wet positive electrode water (C) curve 78,

a wet negative electrode water (D) curve 80,

both wet electrodes water (E) curve 82 in FIG. 2; and

a lower light oil (F) curve 84,

a middle turpentine (G) curve 86, and

an upper 75% ethanol, water and over 50% acetone mixture (H) curve 88 inFIG. 3.

It is noted that curves 80 and 82 each has only the curve points shown,without the curve line, for ease of illustration.

A linen fabric, and a gap of 10 centimeters, was preferably used in thetests for the data of FIGS. 2 and 3. A cotton fabric was also used. Thetests covered various liquids in respective substrates, including waterof curves 78, 80, 82, in FIG. 2, and light oil of curve 84, turpentineof curve 86, and a mixture of 75% ethanol, water and over 50% acetone ofcurve 88 in FIG. 3. The tests also covered a non-liquid, dry conditionin curve 76. The tests using water in the substrate included threetests, including a first test with the water in the substrate, on thepositive electrode of curve 78, a second test with the water in thesubstrate on the negative electrode of curve 80, and a third test withthe water in substrates on both the positive and negative electrodes ofcurve 82.

In summary, the invention relates to a method and apparatus fordetecting with relative great sensitivity even slight amounts ofmoisture in a fabric 66, or other porous material, by using an electricfield. A very sharp increase in current occurs in an electric fieldgreater than about 1,000 volts per centimeter (v/cm.), when relativelyslight moisture is present in the substrate or sample 66, compared tothe current when the substrate is dry. If substrates are placed on bothelectrodes, the current is greater than for either electrode alone.

The electrode disks 50, 52 are disposed parallel to each other. Support12 is an insulator. Current, which passes between disks, 50, 52, passesthrough a vapor from the liquid of the substrate 66. Such current can bemeasured with relatively great accuracy by meter 70, which is aconventional current meter. Coils 22, 24, are conventional heater wirecoils, which are wound on respective posts 42, 44 of insulatingstructure 12.

In FIGS. 2 and 3, test results are shown. In (B) curve 76, results for aperfectly dry cloth substrate show little or no current on the amperescale and the E_(V) scale. In (C), (D) and (E) curves 78, 80, 82, slightdampness produced a sharp rise in current. Such dampness or wetness canproduce a current of up to 100,000 times the current measured fordryness or slight dampness.

It is noted that if a damp fabric is placed on the lower disk and apaddle which is composed of polystyrene insulating material and which ispassed between the disks 50, 52, the ions or charge carriers producedfrom the damp fabric are blocked and cannot reach the opposite disk 52,whereby the current drops to near zero.

In FIG. 3, in (F) curve 84, test results for light oil are shown. In (G)curve 86, test results for turpentine are shown. In (H) curve 88, testresults for a mixture of 75 percent strength ethanol plus water plusover 50 percent strength acetone are shown.

Besides linen fabric, other materials for the substrate 66 work well,including wet cotton, wet paper napkin, wet toweling, wet sheet sponge,wet nylon pad and wet nylon webbing. Wetted wire screening also workswell. Fine layers of water condensation which is placed on the electrodedisks 50, 52 also works well.

Liquid water alone, when placed on the bare electrode disk 50, without afabric or like substrate, does not work; and gives a test result ofabout zero current.

Some volatile liquids, including acetone and ethanol, give a smallcurrent, when placed on the bare electrode disk 50.

The advantages of assembly 10 and its related method are indicatedhereafter.

(A) Assembly 10 can operate relatively fast for testing samples.

(B) Assembly 10 avoids the prior art problem of slow operation intesting samples.

(C) Assembly 10 can test for dampness in many types of fabrics and manytypes of porous materials.

(D) Assembly 10 can test for dampness due to many types of liquids infabrics including organic liquids and inorganic liquids.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes may be made withinthe purview of the appended claims without departing from the true scopeand spirit of the invention in its broader aspects.

The embodiments of an invention in which an exclusive property or rightis claimed are defined as follows:
 1. A fabric wetness detectorcomprising:a support structure; a pair of spaced electrodes havingopposite faces separated by a gap of selective dimension for receivingtherebetween a fabric portion to be tested; and a current sensorconnected to the pair of electrodes for measuring a current passingthrough the gap and fabric portion during an application of a voltagefrom a power supply above approximately 1,000 volts per gap centimeterto the electrodes.
 2. The detector of claim 1, wherein the gap is atleast a fraction of a centimeter in thickness.
 3. The detector of claim1, wherein the fabric is a material like linen or cotton, and the fabricdampness to be tested is water moisture in the fabric, and the gapthickness is about 10 centimeters.
 4. The detector of claim 1, whereinthe support structure includes a lower horizontal wall, a vertical wallsupported by the lower horizontal wall, and an upper horizontal wallsupported by the vertical wall.
 5. The detector of claim 4, wherein thesupport structure is composed of a polystyrene insulating material. 6.The detector of claim 4, wherein the vertical wall has at least threecutouts forming at least two posts for supporting heater coils.
 7. Thedetector of claim 1, wherein the pair of spaced electrodes include alower rod, an upper rod, a lower disk fixedly connected to the lowerrod, and an upper disk fixedly connected to the upper rod, and whereinthe disks have the electrode faces.
 8. The detector of claim 7, whereinthe lower rod and disk and upper rod and disk are coaxial along a commonvertical centerline, and wherein the lower rod is fixedly connected tothe support structure, and the upper rod and disk are adjustablerelative to the lower rod and disk for adjusting the thickness of thegap.
 9. The detector of claim 1, wherein the current sensor includes avoltage source having a pair of connectors connected in series to thepair of electrodes, and through a current meter.
 10. The detector ofclaim 6, including heater means having a pair of vertical heater coils,said coils being wound respectively on said posts, for heating the postsand vertical wall in order to prevent wall condensation for preventing ashort circuit around the electrodes.
 11. A process for sensing moisturein a porous material including the steps of:placing the porous materialto be tested between a pair of high voltage electrodes separated by agap having a thickness of about ten centimeters; applying a voltagepotential across the pair of electrodes, said potential being between10,000 volts to 60,000 volts; and measuring the current passing throughthe gap between the electrodes during the application of voltage,whereby a relatively high current indicates moisture in the porousmaterial.
 12. A process of detecting wetness in a porous material due toa liquid in the porous material, including the steps of;placing theporous material with the wetness between a pair of high voltageelectrodes separated by a gap having a thickness of selective number ofcentimeters; applying a voltage potential across the pair of electrodes,said potential being between 1,000 volts per centimeter of gap thicknessto 6,000 volts per centimeter of gap thickness; and measuring thecurrent passing through the gap between the electrodes during theapplication of the voltage, whereby a relatively high current duringvoltage application indicates wetness in the porous material.